146 lines
7.5 KiB
HTML
146 lines
7.5 KiB
HTML
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<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns:MadCap="http://www.madcapsoftware.com/Schemas/MadCap.xsd" MadCap:lastBlockDepth="6" MadCap:lastHeight="94" MadCap:lastWidth="853" MadCap:disableMasterStylesheet="true" MadCap:tocPath="" MadCap:InPreviewMode="false" MadCap:PreloadImages="false" MadCap:RuntimeFileType="Topic" MadCap:TargetType="WebHelp" lang="en-us" xml:lang="en-us" MadCap:PathToHelpSystem="../../../" MadCap:HelpSystemFileName="Default.xml" MadCap:SearchType="Stem">
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<head><title>RANDOM</title>
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<link href="../../SkinSupport/MadCap.css" rel="stylesheet" />
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<link href="../../Resources/Stylesheets/BSE_Help.css" rel="stylesheet" />
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<script src="../../SkinSupport/MadCapAll.js" type="text/javascript">
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</script>
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</head>
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<body>
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<h1 class="code">RANDOM</h1>
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<div class="ImagePlusCaption">
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<div class="Col2">
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<p>
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<img src="../../graphics/pgm_icon1.gif" border="0" alt="BS1 icon" title="BS1 icon" />
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<img src="../../graphics/pgm_icon2.gif" border="0" alt="BS2 icon" title="BS2 icon" />
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<img src="../../graphics/pgm_icon2e.gif" border="0" alt="BS2e icon" title="BS2e icon" />
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<img src="../../graphics/pgm_icon2sx.gif" border="0" alt="BS2sx icon" title="BS2sx icon" />
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<img src="../../graphics/pgm_icon2p.gif" border="0" alt="BS2p icon" title="BS2p icon" />
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<img src="../../graphics/pgm_icon2pe.gif" border="0" alt="BS2pe icon" title="BS2pe icon" />
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<img src="../../graphics/pgm_icon2px.gif" border="0" alt="BS2px icon" title="BS2px icon" />
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</p>
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</div>
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<p style="text-align: right;"><a href="../ExampleTopics/RandomEx.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">RANDOM Examples</a>
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</p>
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<p> </p>
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</div>
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<p class="clear"> </p>
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<p> </p>
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<p class="PlainText">Syntax: <span class="keyword_in_text">RANDOM</span> <![CDATA[ ]]><i>Variable</i></p>
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<h2>Function</h2>
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<p class="PlainText">Generate a pseudo-random number.
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</p>
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<ul>
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<li value="1"><b><i>Variable</i></b> is a variable (usually a word) whose bits will be
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scrambled to produce a random number. <i>Variable</i> acts as <span class="keyword_in_text">RANDOM</span>'s
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input and its result output. Each pass through <span class="keyword_in_text">RANDOM</span> stores the next
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number, in the pseudo-random sequence, in <i>Variable</i>.</li>
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</ul>
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<h2>Explanation</h2>
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<p class="PlainText"><span class="keyword_in_text">RANDOM</span> generates pseudo-random numbers ranging from 0 to 65535. They're
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called "pseudo-random" because they appear random, but are generated by a logic
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operation that uses the initial value in <i>Variable</i> to "tap" into a sequence
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of 65535 essentially random numbers. If the same initial value, called the "seed",
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is always used, then the same sequence of numbers is generated. The following
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example demonstrates this:</p>
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<p>
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<img src="../../graphics/bs1_inline.gif" border="0">
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</img>
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</p><pre class="BScode" xml:space="preserve">
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SYMBOL result = W1
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Main:
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result = 11000 ' set initial "seed" value
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RANDOM result ' generate random number
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DEBUG result ' show the result on screen
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GOTO Main
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</pre>
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<p>
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<img src="../../graphics/bs2all_inline.gif" border="0">
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</img>
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</p><pre class="BScode" xml:space="preserve">
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result VAR Word
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Main:
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result = 11000 ' set initial "seed" value
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RANDOM result ' generate random number
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DEBUG DEC ? result ' show the result on screen
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GOTO Main
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</pre>
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<p class="PlainText">In this example, the same number would appear on the screen over and over again.
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This is because the same seed value was used each time; specifically, the first
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line of the loop sets result to 11000. The <span class="keyword_in_text">RANDOM</span> command really needs
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a different seed value each time. Moving the "Result =" line out of the loop will
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solve this problem, as in:</p>
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<p>
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<img src="../../graphics/bs1_inline.gif" border="0">
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</img>
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</p><pre class="BScode" xml:space="preserve">
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SYMBOL result = W1
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Setup:
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result = 11000 ' set initial "seed" value
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Main:
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RANDOM result ' generate random number
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DEBUG result ' show the result on screen
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GOTO Main
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END
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</pre>
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<p>
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<img src="../../graphics/bs2all_inline.gif" border="0">
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</img>
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</p><pre class="BScode" xml:space="preserve">
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result VAR Word
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Setup:
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result = 11000 ' set initial "seed" value
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Main:
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RANDOM result ' generate random number
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DEBUG DEC ? result ' show the result on screen
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GOTO Main
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END
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</pre>
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<p class="PlainText">Here, result is only initialized once, before the loop. Each time through the
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loop, the previous value of result, generated by <span class="keyword_in_text">RANDOM</span>, is used as the
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next seed value. This generates a more desirable set of pseudo-random numbers.</p>
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<p class="PlainText">In applications requiring more apparent randomness, it's necessary to "seed"
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<span class="keyword_in_text">RANDOM</span> with a more random value every time. For instance, in the
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example program, <span class="keyword_in_text">RANDOM</span> is executed continuously
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(using the previous resulting number as the next seed value) while the program
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waits for the user to press a button. Since the user can't control the timing of
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button presses very accurately, the results approach true randomness. </p>
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<div class="Col2">
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<div class="MasterFoot">
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<p MadCap:conditions="BSEconditions.BSEWebHelp (Primary)-INCLUDE"><a href="../../HomeTopics/HomePage.htm">Go to Welcome page</a>
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<div class="MasterFoot">
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<p style="text-align: right;"><span class="ContactInfoProjectName">BASIC Stamp Help</span> <![CDATA[ ]]><span class="ContactInfoVersion#">Version 2.5.4</span> <![CDATA[ ]]></p>
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<p style="text-align: right;">Copyright © <span class="ContactInfoCompanyName">Parallax Inc.</span></p>
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<p style="text-align: right;"><span class="SystemShortDate">8/8/2012</span>
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